cmd/internal/obj/arm64: fix assemble fcsels/fcseld bug

The current code treats the type of SIMD&FP register as C_REG incorrectly.

The fix code converts C_REG type into C_FREG type.

Uncomment fcsels/fcseld test cases.

Fixes #21582
Change-Id: I754c51f72a0418bd352cbc0f7740f14cc599c72d
Reviewed-on: https://go-review.googlesource.com/58350Reviewed-by: Cherry Zhang <cherryyz@google.com>
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/cmd/asm/internal/asm/testdata/arm64enc.s

@@ -406,8 +406,8 @@ TEXT asmtest(SB),DUPOK|NOSPLIT,$-8
    FCMPES $(0.0), F29                         // b823201e
    FCMPED F13, F10                            // 50216d1e
    FCMPED $(0.0), F25                         // 3823601e
-   // FCSELS EQ, F26, F27, F25                // 590f3b1e
-   // FCSELD PL, F8, F22, F7                  // 075d761e
+   FCSELS EQ, F26, F27, F25                   // 590f3b1e
+   FCSELD PL, F8, F22, F7                     // 075d761e
    //TODO FCVTASW F21, R15                    // af02241e
    //TODO FCVTAS F20, ZR                      // 9f02249e
    //TODO FCVTASW F6, R11                     // cb00641e

src/cmd/internal/obj/arm64/asm7.go

@@ -536,7 +536,7 @@ var optab = []Optab{
 	{AFCMPS, C_FREG, C_FREG, C_NONE, 56, 4, 0, 0, 0},
 	{AFCMPS, C_FCON, C_FREG, C_NONE, 56, 4, 0, 0, 0},
 	{AFCCMPS, C_COND, C_FREG, C_VCON, 57, 4, 0, 0, 0},
-	{AFCSELD, C_COND, C_REG, C_FREG, 18, 4, 0, 0, 0},
+	{AFCSELD, C_COND, C_FREG, C_FREG, 18, 4, 0, 0, 0},
 	{AFCVTSD, C_FREG, C_NONE, C_FREG, 29, 4, 0, 0, 0},
 	{ACLREX, C_NONE, C_NONE, C_VCON, 38, 4, 0, 0, 0},
 	{ACLREX, C_NONE, C_NONE, C_NONE, 38, 4, 0, 0, 0},